This invention relates to a gear shift mechanism which uses fluid pressure to carry out a gear shift operation and a damper device for the gear shift mechanism.
A gear shift mechanism, as an example, is disclosed in Japanese Patent Application No. 62-110061. The gear shift mechanism is so arranged that a torsional damper device, a gear shift mechanism and an oil pump are disposed around a main shaft. The torsional damper device is connected with the crank shaft of an engine and an end of a main shaft. The oil pump is located at the other end of the main shaft. When the main shaft rotates, fluid pressure is produced and supplied to the gear shift mechanism through an internal orifice of the main shaft. The gear shift mechanism is arranged between the torsional damper device and the oil pump to change the rotation rate of the main shaft.
Thus, in such a conventional gear shift device the gear shift mechanism and the oil pump are both connected with the torsional damper device through the same main shaft. However, in the prior gear shift device, there still exists a so-called "neutral noise" caused by the shift mechanism during the operation of the shift mechanism. This "neutral noise" is produced when a very small change of torque is delivered to the gear shift mechanism at a time when the device is not subject to a driving torque. In other words, the "neutral noise" comes from the striking of the gear teeth of the gear shift mechanism.
Therefore, if the torsional rigidity of the torsional damper device is kept low enough to absorb the slight change of torque delivered to the gear shift mechanism, the "neutral noise" can be prevented.
However, in the prior gear shift mechanism, even though the gear shift mechanism is in a neutral state, since the torque necessary for driving the oil pump acts on the torsional damper device, it is difficult to have a very low torsional rigidity for the torsional damper device.